Ion exchange and the thermodynamics of intracrystalline sorption I. Energetics of occlusion of argon and nitrogen by faujasite-type crystals

The occlusion of argon and of nitrogen has been investigated in a variety of ion-exchanged, synthetic, faujasite-type crystals, over the temperature range 173 to 273 °K and for amounts sorbed between 0 and 0.3 of saturation (A in Li-, Na-, K- Ca-, Sr- and Ba-zeolite) and between 0 and 0.5 of saturation (N2 in Li-, Na-, and K-zeolite). The behaviour observed depends both on the cation present in the crystal and upon the sorbate. In all cationic forms the affinities and heats of intercalation for nitrogen are considerably above those for argon. The crystals behave as energetically homogeneous sorbents for A in Na-, K- and Ba-forms and for N2 in the K -form. The heat of occlusion depends upon amount sorbed, to a greater or lesser degree, for A in Li-, Ca- and Sr-faujasites and for N2 in the Li- and Na-forms. Where energetic heterogeneity arises it is more noticeable in the case of nitrogen sorption. The isosteric heats of sorption of nitrogen are also distinguished from those of argon by showing considerable temperature coefficients. The data for both sorbates have been analyzed in terms of dispersion, repulsion, polarization and quadrupole interactions, and the different behaviour of each sorbate interpreted.